1. Field of the Invention
Claimed is a dealuminated catalyst carrier, a process for producing the catalyst carrier and a process for hydrating C2- or C3-olefins with water in the presence of a catalyst which comprises this catalyst carrier impregnated with acid.
2. Description of the Prior Art
It is known that olefins of low molecular mass which are linear or have only few branches can be converted to alcohols by a reaction with steam in the gas phase under the application of high temperatures and pressures. Of significance for large scale is the synthesis of ethanol from ethene and of isopropanol from propane. The production of these alcohols takes places in the presence of acidic catalysts, wherein usually a catalyst carrier consisting of an alumosilicate and a silicate material is used, which has been impregnated with phosphoric acid, respectively.
The material of the catalyst carrier is usually made up of pure silicic acid, such as, for example, silica gel (U.S. Pat. No. 2,579,601) or consists of silicic acid with a varying amount of alumina (U.S. Pat. No. 3,311,568) and consists of pure lattice-layer silicates (sheet-structure silicates), such as, for example, those containing montmorillonite (DE 29 09 491), respectively.
Apart from these phosphoric acid-containing catalyst carriers, also zeolithic materials are used (EP 0 323 269 B1) or other acidic catalysts, such as, for example, zircon phosphate (GB 00 55 34).
Until now, for carriers that are based exclusively on silicic acid in the form of silica gel, the mechanical hardness is questionable over a longer period of time. Aluminium/containing catalyst carriers or those consisting of only alumina show a noticeably higher long-term stability, but they have the immense disadvantage that aluminium is leached out from the catalyst carrier during the hydration reaction due to the effect of phosphoric acid. The aluminium ends up in the succeeding apparatuses as poorly soluble sedimentations in form of aluminium phosphate. These apparatuses thus are gradually blocked.
In DE 1 156 772 a process is described for reducing the aluminium content of the lattice-layer silicate by reaction with hydrochloric acid. However, even after intensive washing with hydrochloric acid, the carrier material still shows the presence of approximately 1 to 2% by weight of aluminium.
In EP 0 578 441 B1 by using a pelletised silicate carrier based on aerosil (Degussa) which does not contain aluminium, a certain long-term stability is achieved. Starting material for the production of aerosil is the relatively expensive silicon tetrachloride. Since materials based on lattice-layer silicates, such as montmorillonite, for example, are natural raw materials which can be excavated from relevant deposits in the earth, these have an obvious advantage over pelletised silicate carriers according to the economic efficiency of the hydrating process.